1. Field of the Invention
The present invention relates to a mold for producing glass articles, and, more particularly to a mold with which molded glass articles exhibiting high precision can be obtained without needing any post-treatment such as polishing or the like after the press molding has been completed.
2. Prior Art
A mold for producing glass articles is known which comprises a mold base made of glass with a glass transition temperature higher than the temperature at which the glass to be molded is pressed. A mold made of glass of the type described above is disclosed in Japanese Patent Laid-Open No. 226825/1987 in which an adhesion-prevention layer made of a carbon film is formed on the glass-made mold base thereof for the purpose of preventing the glass to be molded from adhering to the mold.
The carbon film serving as the adhesion-prevention layer in the glass mold disclosed in Japanese Patent Laid-Open No. 226825/1987 is coated on the surface of the glass-made mold base by a vacuum evaporation method, sputtering method, ion-plating method or the like. The inventors have found in fact that the following problems arise with the method in which the surface of the glass-made mold base is coated with such a carbon layer, since the adhesive force of the carbon film to the glass-made mold base is insufficient, causing this carbon film to be separated with time elapsed.
(a) The carbon film cannot maintain its function as the adhesion-prevention layer for a long time. Therefore, the life of the mold is too short. PA1 (b) An excessive rough surface can be generated in the surface of the mold, causing the accuracy of the shape to deteriorate. Therefore, desired molded glass articles exhibiting excellent precision and satisfactory optical characteristics cannot be obtained. PA1 a glass-made mold base which contains silicon dioxide as a main component and has a working surface which corresponds to the shape of the glass article to be produced;